Heat exchangers are devices designed to transfer heat between two or more fluids—i.e., liquids, vapors, or gases—of different temperatures. Depending on the type of heat exchanger employed, the heat transferring process can be gas-to-gas, liquid-to-gas, or liquid-to-liquid and occur through a solid separator, which prevents mixing of the fluids, or direct fluid contact.

Heat exchangers are used in many engineering applications, such as refrigeration, heating and airconditioning systems, power plants, chemical processing systems, food processing systems, automobile radiators, and waste heat recovery units.